Questions and Answers
What is the typical thickness range of the stratum corneum, the outermost layer of the skin?
10 μm - 20 μm
Which cells in the epidermis produce and distribute melanin granules?
Melanocytes
What is the function of Langerhans' cells in the skin?
Defense mechanisms operated by the immune system
Which fibrous proteins are embedded in the dermis?
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Why does the dermis require an efficient blood supply?
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How far does the blood supply of the dermis reach from the skin surface?
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What is the primary function of nitric oxide in relation to skin pathogens?
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Why is the intact skin considered an effective barricade?
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Which type of UV light is the most damaging to the skin when exposed to sunlight?
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What main reaction follows irradiation of the skin with UV light?
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How does the skin primarily help maintain the body temperature at 37°C in high temperatures?
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What is a primary target region for dermatologists according to the text?
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What is the primary effect of topical treatments on the skin?
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In what layer of the skin do emollient preparations work to restore softness?
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Which type of skin absorption is crucial in transdermal drug delivery systems?
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What is the primary goal of systemic drug delivery through the skin?
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Which law describes the rate of drug transport across the stratum corneum?
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What is the main purpose of transdermal therapeutic systems?
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Which method involves designing a prodrug with an optimal partition coefficient for entering the skin barrier?
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What is the purpose of chemical potential adjustment in circumventing the horny layer barrier?
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Which method may produce supersaturated solutions leading to a theoretical maximum flux increase?
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How is the drug flux through the skin related to its activity in the vehicle according to the text?
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What is the primary function of the thickened skin in ichthyosis?
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Which method involves the use of high-velocity particles (Powderject) to circumvent the horny layer barrier?
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How does the skin of children differ in terms of permeability compared to adult tissue?
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How can skin regional sites affect cutaneous permeability?
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In what way can supersaturated preparations be described according to the text?
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Why might treating premature infants with caffeine via topical application be advantageous?
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How does an increased blood flow affect transdermal absorption?
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Why is facial skin generally more permeable than other body sites?
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Study Notes
Skin and Transdermal Delivery
- The skin consists of three layers: the epidermis, dermis, and subcutaneous tissue
- The epidermis is the outermost layer, comprising 15-20 rows of flat, dead, keratinized epidermal cells
- The dermis is 3-5 mm thick and consists of a matrix of fibrous proteins, blood vessels, and nerve endings
- The dermis needs an efficient blood supply to convey nutrients, remove waste products, and regulate pressure and temperature
Barrier Function of the Skin
- The intact skin is a very effective barricade due to the diffusional resistance of the horny layer and the permeable appendageal shunt route
- The horny layer is very impermeable to most chemicals and usually contributes the rate-limiting step in transdermal absorption
- The skin is the primary organ responsible for maintaining the body at 37°C
Skin Function and Temperature Regulation
- At high temperatures, the body loses heat through blood vessel dilation, eccrine sweat gland secretion, and evaporation
- At low temperatures, the body conserves heat by shutting down peripheral circulation and generating energy through shivering
Target Regions for Dermatologists
- Skin surface
- Epidermis
- Dermis
- Subcutaneous tissue
- Systemic circulation
Skin Age and Permeability
- Skin of young and elderly is more permeable than adult tissue
- Children and premature infants have greater surface area per unit body weight, making them more susceptible to toxic effects of drugs and chemicals
Factors Affecting Transdermal Absorption
- Changes in peripheral circulation could affect transdermal absorption
- Regional skin sites have variations in cutaneous permeability depending on the thickness and nature of the SC and density of skin appendages
- Facial skin is generally more permeable than other body sites
- The horny layer barrier can be circumvented by methods such as prodrugs, chemical potential adjustment, hydration, ultrasound, iontophoresis, stratum corneum removal, microneedles, penetration enhancers, ion pairs, and high-velocity particles
